While there are many patents on sealant compositions for pneumatic tires, three patents: U.S. Pat. Nos. 4,116,895; 4,426,468; and 4,616,048 provide basic information on the field. An often used curative for the sealant compositions is a quinoid type system, which generally comprises a quinoid and a crosslinking activator. The quinoids and their activators are set forth in U.S. Pat. No. 4,426,468 ('468 column 5, line 28, through column 6, line 5). In U.S. Pat. No. 4,616,048 ('048) the crosslinking activator of the '468 patent is described as a cocuring agent "B" and the concept of a optional polar solvent accelerator is introduced (column 5, line 33, through column 6, line 8). The '468 patent in column 5, lines 28-29, explains the quinoid cure system depends on crosslinking through nitroso groups.
In U.S. Pat. No. 4,116,895 ('895) column 6, lines 4-13, the author explains that if the amount of crosslinking is too low the sealing properties at high temperature are ineffective while a crosslink density that is too high also prevents the sealant from functioning.
In the '468 patent column 2, line 32, through column 3, line 18, the author explains that tire sealants benefit from the optimization of three properties: tensile strength, elongation, and crosslink density. The examples of the '468 patent illustrate how the three properties can be correlated with various aspects of tire sealant performance. In the '468 patent the quinoid is diluted in cyclohexanone and then added to a butyl rubber and Piccotac component which have been premixed in hexane at about 50 wt. % solids.
The '048 patent teaches a method of dispersing quinoid curing agents in a rubber composition that results in a uniform fine dispersion of the quinoid. In the examples of the '048 patent (column 7, line 49, through column 8, line 20) the quinoid was made up as a 5 wt. % solution with surfactants in tetrahydrofuran, which was then mixed with a majority of the rubbers predissolved in hexane. This is consistent with the Detailed Description (column 4, line 31, through column 5, line 6) where the addition of the quinoid as a dissolved solution during mixing of the rubber in solvent results in the precipitation of the quinoid curative as a fine dispersion. Column 5, lines 39-42, specify that the solvent for the quinoid not only has to be a reasonably good solvent for the quinoid but it must be compatible with the masterbatch solvents in the rubber cement. Table II of the '048 patent illustrates the "solution method" increases the maximum torque of samples over samples prepared by the "conventional mixing" and decreases the time to reach maximum torque. These results imply the quinoid is more effective as a curative when finely dispersed. In Table IIIA the "solution method" results in lower swell ratios and higher solvent clarity which implicates more effective and uniform crosslinking. In Table IIIB the "solution method" resulted in enhanced solvent clarity and less microgel indicating more uniform crosslinking.